(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

An object gives out a spectral line of 919nm compared to that of 589nm in a laboratory. It has a brigtness of 1.2 x 10^{-11}W m^{-2}. The objective is to find out the brightness of the object if it were at 700 Mpc.

2. Relevant equations

1. Z (redshift)= change in wavelength / original wavelength

2. V= Z X C

3. V= H_{0}D

4. F= L / 4 pi r^{2}

3. The attempt at a solution

The redshift value I find to be 0.56 using equation 1. Using this I calculate the speed as 168000 km s^{-1}using equation 2. I then work out the distance of the object to be 2400Mpc using equation 3 rearranged. now from here do I use equation 4 to calculate the luminosity and then change the distance to 700Mpc or do I divide 2400Mpc by 700Mpc to get how many times closer the object will be square the answer ( 3.43^{2}) and times it by the original brightness 1.2 x 10^{-11}W m^{-2}?

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# Brightness of distant galaxies problem

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